The present invention relates to a pattern formation material and a pattern formation method for use in semiconductor fabrication process and the like.
In accordance with the increased degree of integration of semiconductor integrated circuits and downsizing of semiconductor devices, there are increasing demands for further rapid development of lithography technique. Currently, pattern formation is carried out through photolithography using exposing light of a mercury lamp, KrF excimer laser, ArF excimer laser or the like. Also, in order to form a fine pattern of a rule of a 0.1 μm or less, and more particularly, of 70 nm or less, use of exposing light of a further shorter wavelength, such as vacuum UV like F2 laser (of a wavelength of a 157 nm band) or extreme UV (of a wavelength of a 1 nm through 30 nm band) as well as use of EB employing EB projection exposure or the like is being studied.
Among these exposing light, extreme UV is particularly promising because it can be used for forming a pattern of a rule of 50 nm or less.
Now, a conventional pattern formation method will be described with reference to FIGS. 2A through 2D.
First, a chemically amplified resist material having the following composition is prepared:
   Base polymer: poly((p-t-butyloxycarbonyloxystyrene) -4.0g(hydroxystyrene)) (wherein p-t-butyloxycarbonyloxy-styrene:hydroxystyrene = 40 mol %:60 mol %)Acid generator: triphenylsulfonium nonafluorobutanesulfonate0.12gSolvent: propylene glycol monomethyl ether acetate20g
Next, as shown in FIG. 2A, the aforementioned chemically amplified resist material is applied on a substrate 1, so as to form a resist film 2 with a thickness of 0.15 μm. Thereafter, as shown in FIG. 2B, the resist film 2 is selectively irradiated with extreme UV 3.
Then, as shown in FIG. 2C, the substrate 1 is annealed with a hot plate at a temperature of 100° C. for 60 seconds. Thus, an exposed portion 2a of the resist film 2 becomes soluble in an alkaline developer because an acid is generated from the acid generator therein while an unexposed portion 2b of the resist film 2 remains to be insoluble in an alkaline developer because no acid is generated from the acid generator therein.
Next, the resist film 2 is developed with a 2.38 wt % tetramethylammonium hydroxide developer. In this manner, a resist pattern 4 with a line width of 0.07 μm made of the unexposed portion 2b of the resist film 2 can be obtained.
In a pattern formation method, a highly accurate optical system is necessary, and in a general optical system for introducing extreme UV to a resist film, the resist film is occasionally irradiated with not only the extreme UV but also longer band light of a wavelength longer than the extreme UV. This is also derived from a light source of the exposing light.
On the other hand, a chemically amplified resist material used in a pattern formation method employing extreme UV as exposing light is set so that an acid can be generated through irradiation with the extreme UV for changing the solubility of a polymer in a developer.
Therefore, in the case where the general optical system is used for irradiating a resist film with extreme UV, when the resist film is irradiated with not only the extreme UV but also the longer band light of a wavelength longer than the extreme UV, the chemically amplified resist material is sensitized to the longer band light. This lowers the optical contrast between an exposed portion and an unexposed portion of the resist film, and as a result, there arises a problem that the resultant resist pattern is in a defective shape.
Accordingly, as shown in FIG. 2D, the conventional resist pattern is in a defective cross-sectional shape. When such a resist pattern in a defective shape is used for etching a target film, the resultant pattern is also in a defective shape.